The invention relates to a breaking apparatus which comprises a percussion device and, in the axial extension thereof, a tool, the percussion device having a percussion piston that is arranged to make reciprocating movements in the axial direction and to strike a strike-receiving surface for providing an impact impulse in the tool, whereby the tool transmits the impact impulse further to a target to be broken, the breaking apparatus also comprises a tool stopper, by which the axial movement of the tool away from the percussion device is limited, the tool stopper comprising at least one stopper element of elastic material, whose cross section is substantially circular and whose cross-sectional central axis is transverse to the longitudinal axis of the tool, and in which breaking apparatus the stopper element is arranged in a space between the tool and a supporting surface, whereby, during the stopping of the tool, the mutual axial movement of the tool and the supporting surface is arranged to provide a volumetric change in said space for the stopper element.
The invention further relates to a tool for the breaking apparatus, which tool is to be arranged in an axial extension of the percussion device in the breaking apparatus, the tool comprising a strike-receiving surface which a percussion piston of the percussion device is arranged to strike so as to provide an impact impulse in the tool, which is arranged to transmit the impact impulse further to a target to be broken, and the breaking apparatus comprises a tool stopper, by which the axial movement of the tool away from the percussion device is limited, whereby at least one stopper element of elastic material is arranged in a space between the tool and the supporting surface, whereby, during the stopping of the tool, the mutual axial movement of the tool and the supporting surface is arranged to provide a volumetric change in said space for the stopper element.
Breaking apparatuses, i.e. percussion hammers, are used for breaking stone, concrete, asphalt, frozen ground, metal slag and other relatively hard materials. Conventionally, the percussion hammers are mounted in place of excavator buckets, and consequently they are operated by excavator hydraulics. Other base machines and mounting frames can be used as well. The breaking apparatus comprises a percussion device, to which a tool is attached. When the apparatus is in operation, a percussion piston of the percussion device moves to and fro by the action of pressure medium, strikes a strike-receiving surface of the tool and provides an impact impulse in the tool. The tool is simultaneously pressed against the target to be broken, whereby the tool penetrates, by the effect of the impact, into the material to be treated and makes the material break or cut, depending on the shape of the tool.
The tool is arranged in the percussion hammer such that, during the use, it can move to and fro for a predetermined distance in the impact direction of the percussion piston. In connection with the tool, there is a so-called tool stopper which holds the tool attached to the percussion device such that the tool cannot fall freely off the percussion hammer, for instance, when the breaking apparatus is transferred and when the tool is not supported against the target. Conventionally the tool stopping is arranged such that longitudinal, elongated grooves are provided on the outer surface of the tool shaft, on the opposite sides thereof. Alternatively, an elongated opening is provided in the tool. The percussion hammer body comprises, in turn, transverse support openings at said grooves or openings and a stopper bolt is inserted in the transverse direction through the support openings in the body and the grooves in the tool. The movement of the stopper bolt is then prevented with respect to the body, but thanks to the grooves, the tool can move in the percussion piston""s direction of movement for a distance limited by the length of the grooves.
When the target is suddenly broken under the tool, or when the tool otherwise penetrates into the material to be broken faster than predicted, for instance in soft stone, a so-called idle stroke is produced. When the idle stroke takes place, the tool is not sufficiently supported to the target to be treated so as to transmit forces produced by the impact impulse to the target to be treated in a normal manner, but the tool must receive the impact mainly by means of the stopper mechanism of the tool. In a conventional stopper solution, in which a groove, an opening or a corresponding stopping surface provided in the tool strikes against the transverse stopper bolts, the stopping is rigid. There is metal against metal in the contacting surface between the tool and the stopper bolts. The tool is stopped at a short distance and consequently the structure of the percussion hammer is subjected to heavy stresses. For instance, binding bolts, with which various blocks of the percussion hammer are generally assembled, are subjected to heavy loads resulting from stopping forces. One solution attempts to damp the stresses resulting from the stopping of the tool by supporting the stopper bolt elastically to the body of the percussion hammer. In that case, when stopping the tool, the stopper bolt can shift for a predetermined distance in the direction of the impact supported by springs or corresponding means. However, these solutions have a disadvantage that the structure is complicated and expensive.
Further, stopper mechanisms based on the use of elastic material have been developed. In one solution, a conventionally mounted stopper bolt consists of two metallic halves, between which there is elastic material to damp the stopping forces. However, in case of a idle stroke it is difficult to provide sufficient damping with an elastic stopper bolt of this kind. In addition, the structure is expensive and difficult to manufacture. For instance, from DE publication 805,268 is still known a bushing, made of an elastic material, which is arranged to be immovable in a circular space provided in a lower end of the percussion device, to encircle the upper end of the tool. The tool then comprises a shoulder, by which the movement of the tool is limited in the direction of the impact. When the tool protrudes over the usual operating range outwardly from the percussion hammer, for instance in case of a idle stroke, the shoulder starts pressing the stop bushing in the radial direction. The circular space for the stop bushing in the body is designed capacious as compared with the volume of the bushing, so that the bushing can change its shape in the circular space as pressed by the shoulder. In one solution, a separate chamber, in which a bushing-like ring of elastic material encircles the tool, is arranged at a lower end of the percussion hammer. The bushing is supported to the chamber only on the outer circumference. The tool shaft has a shoulder by which shearing/pressing stress is caused to the elastic ring. This has a drawback that the chamber at the lower end of the percussion hammer increases the length of the percussion hammer. Hence, the tool must be longer, which may cause problems in supporting the tool. Apart from the longitudinal direction, the arrangement of shearing/pressing type requires a considerable space around the tool as well, and as a consequence, the solution increases the total outer dimensions of the percussion hammer, which makes the apparatus difficult to operate.
The object of the present invention is to provide a novel and improved arrangement for stopping a tool of a breaking apparatus.
The breaking apparatus according to the invention is characterized in that a stopper element is a substantially circular piece in cross-section, that the cross-sectional central axis of the stopper element is transverse to the longitudinal axis of the tool, and that when stopping the tool the stopper element is arranged to rotate about its said central axis and to move in the direction of the impact of the percussion device, and while rotating to change its cross-sectional shape in a space with reducing capacity.
The tool according to the invention is characterized in that the upper part of the tool comprises a bushing-like guide part, whereby the tool and the percussion device can be partly nested, that the upper part of the tool comprises a shoulder portion that widens in the radial direction of the tool, the shoulder portion being arranged to affect the stopper element having a substantially circular cross section, which stopper element is arranged in a space between the tool and the supporting surface, and whose cross-sectional central axis is transverse to the longitudinal axis of the tool, and that when stopping the tool said shoulder portion of the tool is arranged to make the stopper element rotate about its cross-sectional central axis and make the tool move in the axial direction and further provide a change in the cross-sectional shape of the element.
The basic idea of the invention is that the movement of the tool in the percussion hammer is limited in the direction of the impact by means of a stopper element made of elastic material. The stopper element is arranged in a space between the tool and a suitably designed supporting surface. When mounted into place, the cross-sectional central axis of the stopper element is transverse to the longitudinal axis of the tool. The supporting surface is further supported substantially immovably to the percussion hammer body or a housing. The cross-section of the stopper element is substantially circular, whereby the element is arranged to revolve about its cross-sectional central axis in the space limited by the tool and the supporting surface when stopping the movement of the tool. Thanks to revolving, the stopper element wears less than in known solutions, wherefore it has a longer service life. The stopper element is preferably a loop, and consequently the space provided for it is ring-shaped. Technically, rotationally symmetrical shapes are less demanding and less expensive to manufacture.
While the stopper element rotates, it changes its cross-sectional shape. The surfaces of the space for the stopper element are designed oblique in the direction of the impact. Thus, the tool exceeding the normal range of operation provides a reduction in the capacity of said space. Advantageously, the oblique surfaces are suitably designed such that a change in the cross-sectional shape of the stopper element and the resulting force that resists the movement of the impact of the tool increase progressively in proportion to the length of travel of the tool, when the tool has exceeded the determined, normal range of operation. The forces resulting from a idle stroke are thus received in a guidelable manner, and the stopping distance is long, up to ten times longer than the stopping distance provided by rigid stopper bolts of metal. The loads, which result from the stopping and to which the structure of the percussion hammer is subjected, thus remain substantially lower. Despite the fact that the stopping distance of the invention is substantially longer than in previous solutions, the rotating stopper element takes clearly less space than the known solutions.
The contacting surface between the stopper element having a substantially circular cross-section and the tool/supporting surface is line-shaped, but when the stopper element flattens under a load, the contact surface becomes larger. The heavier the load, the larger the contact surface is. Thus the adaptable stopper element balances surface pressures on counterparts. Thanks to the above-mentioned facts, the forces, to which the structure of the percussion hammer is subjected on stopping the tool, are lower than previously and they are in better guide, and consequently the percussion hammer need not be designed so sturdy and massive. Therefore, the structure can be lighter and less expensive to manufacture. In addition, it is easier to handle this kind of percussion hammer. The design and selection of the material of the stopper element, and further the design of the tool shoulder and the supporting surface, allow to affect the stopping of the tool and the damping of the stopping forces in a relatively simple manner. The stopper element is a simple wearing piece, which is inexpensive to manufacture and easy to change.
Further, the basic idea of a preferred embodiment of the invention is that the tool and the supporting surface are designed such that at the end of the stopping event the space for the stopper element is substantially closed. The elastic stopper element thus substantially adapts to the shape of said closing space by the effect of a compressive force. When the stopper element is of elastic material, such as rubber, which is substantially incompressible, the tool cannot move on any further and it finally stops in this extreme position.
According to a second preferred embodiment of the invention there is a bushing-like guide portion at the upper end of the tool. The tool and the lower end of the percussion device are partly nested. The upper end of the tool is large in diameter, and therefore the contacting surface between the stopper element and the tool, and correspondingly between the stopper element and the supporting surface can be large. The tool can also be shorter and sturdier than before.
In a third preferred embodiment of the invention, the supporting surface is provided in a lower part of the housing, on the inner surface thereof. A shoulder having an oblique surface is provided in the upper part of the tool. In this construction, the stopper element is arranged in a space between the tool and the supporting surface provided in the housing. The housing thus protects the percussion hammer well against bumps and impurities. If necessary, the stopper element can also serve as a seal between the tool and the housing.
The basic idea of a fourth preferred embodiment is that the upper end of the tool is bushing-like and it extends round the lower part of the percussion device. The supporting surface is provided in the percussion device body, and a groove is provided correspondingly in the upper part of the tool, whereby the stopper element is arranged in a space between the percussion device body and the tool.
Further, the basic idea of a fifth preferred embodiment is that the lower part of the housing extends below the front end of the percussion device. The supporting surface and the stopper element are then located in the front end of the housing, the guide bushing of the tool being above them. The oblique surface between the tool shaft and the bushing-like portion presses the stopper element against the supporting surface as the tool is stopped.